The deposition of coatings on a substrate is conventionally accomplished using either a plasma torch which creates a plasma plume that envelopes the substrate, such as in the device disclosed in U.S. Pat. No. 4,555,611 to Moll, or an electric arc generated between a cathode and an anode which creates an ionized plasma stream in the vicinity of the substrate. Devices incorporating these methods are well known to those skilled in the art.
The main disadvantage to any apparatus of this type is the limited length of the reaction zone. In the case of for example a plasma jet or plume, such as that described in U.S. Pat. No. 4,555,611 to Moll, the reaction zone is limited by the input power of the source.
In the case of an arc-generated plasma stream, such as that described in European Patent No. 478,909 A1 to Balzers Aktiengesellschaft, the homogeneous reaction zone is limited to the stable portion of the arc, and the ionized plasma tends to be denser in the cathode region. In both cases this severely limits the size of the substrate that can be coated and the quality or uniformity of the coating. Additionally, because the arc is dispersed throughout the apparatus and not well confined, in order to simultaneously process multiple substrates, the deposition process must be carried out at low pressures, reducing plasma density and commensurately reducing the efficiency and rate of deposition.